REST API created, exposed and consumed in Outsystems

I'm trying to implement a REST API on an eSpace (to expose it) using the information from the Outsystems help, but I'm having a problem consuming it on another Outsystems application. Can anyone help me on this?
I did the following:

Then, after publishing it, I opened the other eSpace from another application and tried to consume my REST API:

How can I proceed? Is there a way to automatically generate the input and inputs?
I tried to set also the Response Format to JSON and I receive this message - "'GetByUsername' method requires an output parameter with 'List' or a Structure data type and the Receive In property set to 'Body' ".

This is my first custom REST API, so I would be grateful if someone could help me on this.